1. Field of Invention
The present invention relates generally to a substrate planarization system and a method for processing a substrate.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to stack multiple devices on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
Two exemplary CMP systems that address these issues are described in U.S. Pat. No. 5,804,507, issued Sep. 8, 1998 to Perlov et al. and in U.S. Pat. No. 5,738,574, issued Apr. 15, 1998 to Tolles et al., both of which are hereby incorporated by reference. Perlov et al. and Tolles et al. disclose a CMP system having a planarization apparatus that is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. The transfer station generally contains a load cup that positions the wafer into one of four processing heads mounted to a carousel. The carousel moves each processing head sequentially over the load cup to receive a wafer. As the processing heads fill, the carousel moves the processing head and wafer through the planarization stations for polishing. The wafers are planarized by moving the wafer relative to a polishing pad in the presence of a slurry or other polishing fluid medium.
The polishing pad may include an abrasive surface. Additionally, the slurry may contain both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.
Optionally, one of the planarization stations may be a buffing station. The buffing station also processes the wafer in a circular motion similar to the planarization station. The buffing station removes surface contamination, such as loosely adhered particles, so that the wafer may be cleaned more effectively after polishing in a cleaning module that may be located adjacent to or remotely from the CMP system.
As the planarization stations are circularly orientated about the carousel, the footprint of rotational polishers is generally compact. Compact, or small footprints, generally allow for more processing equipment to be utilized in process areas, and contribute to lower factory overhead and greater wafer throughput.
Another system disclosed in U.S. Pat. No. 5,908,530, issued Jun. 1, 1999, to Hoshizaki et al., which is hereby incorporated by reference, teaches an apparatus for planarizing wafers wherein the wafer is subjected to uniform velocity across the wafer surface with respect to the abrasive surface. The wafer""s motion is provided by a first linear drive and a second linear drive configured to provide x/y motion to a wafer carrier coupled to one of the linear drives. In one aspect, the wafer can be moved in an orbital pattern.
A polishing head is coupled to the wafer carrier to retain the wafer during polishing. Generally, the wafer is positioned in the polishing head by a dedicated load cup that also receives the polished wafers from the polishing head after processing. The polishing head generally stands idle while finished wafers are removed from the load cup and replaced with unpolished wafers.
Since the wafer does not rotate during polishing, all the points on the wafer are subject to a uniform velocity relative to the polishing surface. The uniform velocity across the wafer surface coupled with a multi-programable lanarization pattern results in a uniform rate of material removal from the wafer surface. In addition, Hoshizaki et al. provides a number of optional routines that allow a user to fine tune material removal from the wafer.
The systems described above can generally utilize polishing pads with and without abrasive finishes. The polishing pads may be stationary or move relative to the wafer. Additionally, abrasive slurry, de-ionized water and other fluids may be delivered to the polishing pad during wafer processing.
While both the rotational and linear planarization systems have proven to be generally robust polishing platforms, the elimination of the dwell time associated with loading and unloading a polishing head would improve the routing time required to process each wafer, and yield a corresponding increase in wafer throughput. The increase in wafer throughput has an advantageous effect on both the manufacturing cost of the devices fabricated on the wafer, and the cost of ownership associated with the polishing system.
Therefore, there is a need in the art for an apparatus that provides higher throughput by minimizing the dwell times during wafer transfer between system components.
Generally, a chemical mechanical planarization system for processing a workpiece such as a semiconductor substrate or wafer is provided. In one embodiment, the planarization system includes a first polishing module having one or more polishing heads for retaining a workpiece and a staging module. A first set of load cups transfers the workpiece between the one or more polishing heads. A first robot has a workpiece gripper that facilitates transfer of the workpiece between the first set of load cups and the staging module.
In another embodiment, a planarization system includes one or more polishing modules and a rotational buffing module. Each polishing module and buffing module has one or more polishing heads for retaining a workpiece during processing. A staging module is used to facilitate transfer of workpieces into and out of the system. A plurality of load cups for transferring the workpiece to and from the polishing heads are positioned such that a robot may transfer workpieces between the load cups and the staging module.
In another aspect, a method for processing a workpiece is also disclosed. In one embodiment, the method comprises the steps of processing the workpiece on a first linear polishing module; and processing the workpiece on a rotational buffing module coupled to the first linear polishing module. In other embodiments, the comprises the steps of transferring the workpiece from a first load cup into a first polishing head; processing the workpiece; and transferring the workpiece from the first polishing head to a second load cup.